tap water
print header

Drinking Water

Nitrates in Drinking Water

Nitrates are colourless, odourless chemicals that occur naturally throughout the environment or as a result of human activities. Nitrates are products of the oxidation of nitrogen as part of the cycle required by all living systems for the production of complex organic modules such as proteins and enzymes. The Ontario Drinking Water Quality Standard for nitrate is 10 mg/L as nitrate-nitrogen. This is the maximum acceptable concentration (MAC) for drinking water.

Agricultural run-off, refuse dump run-off and contamination with human or other animal wastes are responsible for the increases in nitrate concentrations in both surface waters and groundwaters. Sources can include:

  • Fertilizer
  • Leachate from garbage dumps
  • Municipal and industrial waste water
  • Septic systems
An elevated level of nitrate in drinking water is primarily a health concern for bottle-fed infants less than six months of age who have not yet developed the ability to properly digest nitrates. This can lead to a rare but very serious condition called methemoglobinemia, or blue baby syndrome. The inability to digest nitrate leads to the production of nitrite, which affects the amount of oxygen carried in the blood, resulting in a bluish tint to the skin. If the level of nitrate in your water is above 10 mg/L, you should use a different water supply to prepare baby formula and food or use ready-to-use formula. Breastfeeding is safe. Breast milk is not affected by nitrates.

The only way to know whether there are nitrates in your drinking water is to have it tested by a licensed laboratory. Municipal drinking water systems are tested regularly but if you draw your drinking water from a well, the health unit recommends testing your well water for nitrates at least once a year. Visit the Ministry of the Environment, Conservation and Parks website for a complete list of accredited laboratories.

It is also recommended that you test your well water for bacteria at least three times a year. Bacterial contamination can be an indicator that surface water is entering your well, which may also contain nitrates. Bacterial testing is free for private homeowners.

Here are a few ways you can help keep your water safe:

  • Improve agricultural practices such as fertilizer storage and manure application.
  • Inspect your septic system every 3-5 years.
  • Avoid activities such as mixing or storing chemicals around water wells.
  • Regularly inspect your well for cracks and evidence of flooding.


If you are further concerned about nitrates in your drinking water, it is recommended that you contact a professional about installing an effective water treatment device to reduce the amount of nitrates in your drinking water. Boiling water will not remove nitrates and will only increase the concentration of nitrates in the water.

Once the level of nitrates in your drinking water is below 10 mg/L, it is safe to resume using water for formula and food preparation for infants less than six months of age.

Did you find what you were looking for today?
What did you like about this page?
How can we improve this page?

If you have any questions or concerns that require a response, please contact Health Connection directly.

Thanks for your feedback.
Failed to submit comment. Please try submitting again or contact us at the Health Unit.
Comment already submitted ...